Separation of aromatics from hydrocarbon streams

ABSTRACT

Aromatic compounds may be separated from paraffin-aromatic mixtures by using a solvent consisting of a solution of an aromatic dissolved in the same aromatic in its protonated form with aluminum chloride, (ArH) (Al2Cl7), wherein a liquid paraffinic phase and a liquid aromatic phase are formed, separating the phases and adding HCl to the aromatic phase to react with the solvent and adjusting the temperature to form a solid phase having the following formula:

Cier

[ SEPARATION OF AROMATICS FROM HYDROCARBON STREAMS [75] Inventor: HarryE. Cier, Baytown, Tex.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

[22] Filed: July 23, 1971 [2l] Appl. No.: 165,599

[52] US. Cl. 208/331, 208/321, 260/674 SE [51] Int. Cl C10g 21/18 {58]Field of Search 208/336, 321; 260/674 SE [56} References Cited UNITEDSTATES PATENTS 3,565,965 2/l97l Walker et al 260/674 SE 3,280,02510/1966 Poe et al 2,842,604 7/l958 Waals et al 260/674 SE 2,838,5836/1958 Schneider 260/674 SE 2,879,313 3/1959 Scott et al 260/669 [451Aug. 28, 1973 Primary ExaminerHerbert Levine Attorney-Thomas B.McCulloch et al.

I 5 7 ABSTRACT Aromatic compounds may be separated from paraffinaromaticmixtures by using a solvent consisting of a solution of an aromaticdissolved in the same aromatic in its protonated form with aluminumchloride, [ArH] [Al Cl,-],wherein a liquid paraffinic phase and a liquidaromatic phase are formed, separating the phases and adding HCl to thearomatic phase to react with the solvent and adjusting the temperatureto form a solid phase having the following formula:

[Ari-1] [AlCl which then may be separated from the aromatic compoundspresent in the mixture. The aromatic identified as Ar in the aboveformula is mesitylene, isodurene, pentamethylbenzene, hexamethylbenzeneor polynuclear aromatics more basic than the mononuclear aromatic. [ArH]AlCl.,] may be used as the solvent in a preferred mode.

14 Claims, 2 Drawing Figures WATER I6 I g 1 PARAFFINIC HYDROCARBONSAr+[ArH:|+[A9 cJ2 EXTRACTION l3 BTX FEED SEWER 40- FILTE'R WATER .I L pc/ 3 26 e- 7 s g l 3| 29 AROMATIC 32 HYDROCARBONS HCQM 'P T0 AKEU SEWERRECYCLE SEPARATION OF AROMATICS FROM HYDROCARBON STREAMS BACKGROUND OFTHE INVENTION consisting of a solution of an aromatic dissolved in thethe same aromatic in its protonated form with aluminum chloridehaving'the formula:

Ar [ArI-I] [Al Cl in which the aromatic compounds in the mixture form anaromatic phase. In its most specific aspects the invention is directedto recovering the solvent by adding HCl to the aromatic phase after itis separated from the paraffinic phase and recovering a solid having thefor mula:

[Ari-I] [AlCl which may then be reused and recycled. I

2. Description of the Prior Art The following listed U. S. Patents wereconsidered in connection with this invention:

While it has been known in the prior art to use HCl as part of thecomplex, none of the foregoing art teaches the formation of a solidphase with the concomitant formation of two liquid phases and separationof the phases for recovery of aromatic products. Also, while the priorart teaches the separation of the paraffinic hydrocarbons from thearomatic hydrocarbons, none of the prior art teaches the separation of asolid solvent phase for recovery of the-desired aromatic hydrocarbonsfrom the rich extract solutions discharging from the extraction tower.The present invention is, therefore, new, useful and unobvious.

SUMMARY OF THE INVENTION The present invention is directed to a processfor separating aromatic compounds from paraffin-aromatic mixtureswherein a particular solvent is used which can be recovered andrecycled. Thesolvent use'd consists of a solution of an aromatic,whichis at least as basic as any of the aromaticcompounds to beseparated from the paraffin-aromatic mixture, dissolved in the samearomatic in its protonated form with aluminum chloride and thus havingthe structure:

This solvent has the capability to dissolve several mols of aromatic inwhat may be termed asolvation shell.

Paraffins are inert and have very low solubility in this protonatedsolvent and hence two liquid phases form. A paraffmic phase may beseparated from the aromatic phase. To recover the solvent it has beenfound according to this invention that the aromatic phase may be treatedwith hydrogen chloride at a pressure and temperature such that 1 mol ofhydrogen chloride together with the equal molar aromatic and protonatedaromatic will form 2 mols of 'a product having the following for mula:

[Arl-I] [A1Cl At theoperatingtemperatu'res (i.e., the temperature oftreating with 'HCl) this product is a'solid and precipitates from theremaining aromatic compounds. Separation may be accomplished by anymeans wherein the liquid and solid are separated such as filtration orcentrifuga'tion. The filtrate is the'des'ired aromatic productcontaining onlyvery small amounts of dissolved solvent. The resultingextract from a water wash of the filtrate is a high purity aromaticproduct. If there are mixtures of aromatics, such as C C-,, and Caromatic compounds, these may be separated by simple distillation. Thesolid product may be recycled by heating and reducing the pressure toreverse the reaction wherein the hydrogen chloride is removed andrecycled with the production of the solvent solution which maylikewisebe recycled.

VARIABLES OF THE INVENTION The extraction of a mixture of paraffins andaromatics is suitably carried out at temperatures from about 0 to aboutC. The temperature at which HCl is added to form the solid (when HCl isused) is from about -80 C to about 20 C.

The aromatic hydrocarbon characterized as Ar is suitably mesitylene,isodurene, pentarnethylbenzene, and 'hexamethylbenzene which may becharacterized as polymethyl aromatic hydrocarbons more basic than thelower aromatic hydrocarbons on the feed mixture. The other trimethyl andtetramethyl benzenes are not as basic as the feed aromatic hydrocarbons.

Suitable feed mixtures which may be treated in accordance with thisinvention are benzene, toluene, and xylenes or mixtures thereof whichfor convenience is termed BTX which may include any or all the aromatichydrocarbons in' the mixture but which may beonly one, such as a mixtureof xylenes or one or two of them, and the corresponding paraffins andnaphthenes. The aromatic hydrocarbons comprise about lOwt. percent toabout percent by wt. of the feed. Other aromatic hydrocarbons andparaffins and/or naphthenes may be used such as those boiling from about60 C F) to about 200 C (400 F).

BRIEF DESCRIPTION OF THE DRAWING The invention will be furtherillustrated by reference to the drawing representing preferred modes andembodiments in which:

FIG. 1 represents a flow diagram of one mode of practicing the inventionwhere HCl is used; and

FIG. 2 represents a mode where HCl is not employed.

DESCRIPTION 'OF THE DRAWING Referring now to the drawing, andparticularly to FIG. 1, numeral 11 designates an extraction column intowhich is fed by line 12 a mixture of benzene, toluene and xylene andnaphthenes and paraffins corresponding thereto. This fraction may boilin the range from about 60 C. to about 160 C. There is also fed intoextraction column 11 by line 13 a suitable solvent which is a solutionof an aromatic such as mesitylene and complexed [ArI-I] [Al Cl Ar beingmesitylene. In extraction column 11, which is suitably fitted withcontacting means such as bellcap trays and is maintained at extractiontemperatures, a raffinate phase and an extract phase are formed, theraffinate phase being withdrawn by line 14 and discharged thereby intosettler 15, into which water is introduced by line 16, which causes aseparation between the paraffinic and any naphthenic hydrocarbons andthe water phase which will contain dissolved HCl and aluminum chloride.The water phase is withdrawn and discharged by line 17.

The extract phase is withdrawn from extraction column 11 by line 18 andintroduced thereby into a mixing vessel 19 equipped with a suitablemixing means 20. I-ICl is introduced by line 23 and the HCl under theconditions of temperature and pressure in vessel 19 form a solid phase.The solid phase is withdrawn with the unsolidified material by line 24into a filtration zone 25, from whence there is withdrawn by line 26filtrate which is treated with water in separation stage 27 introducedby line 28, which causes a separation of water from the C C and C,aromatic hydrocarbons. Any aluminum chloride and I-ICl is withdrawn inthe water phase and discharged from zone 27 by line 29. The C C and Chydrocarbons withdrawn by line 30 may be suitably distilled to recoverbenzene, toluene, and xylenes.

The solid phase in filtration zone is withdrawn by line 31 surrounded byheating jacket 32 through which is circulated a suitable heating fluidto liquefy the solid phase which is discharged by line 35 into a drum 36from whence HCl is withdrawn by line 37 by compressor 38 which connectsto line 23. HCl makeup may be introduced by line 39. Withdrawing theI-ICl from drum 36 results in formation of the complex Ar+[ArI-I- ][AlCl which is recycled to line 13 by line 40 for reuse in the process.

Referring now to FIG. 2, either the solvent [ArI-I- ][AlCl in extractionand recovery, the solvent [ArI-I- ][Al Cl in the extraction section, and[Ar][AlCl in the recovery section may be used. In the first case, it ispreferred that the solvents employed be mesitylene, hexamethylbenzene,isodurene, or pentamethylbenzene. In the second case, use of the abovenamed aromatics in the form [Arl-I][Al,Cl with an extra mol of thearomatics may be used. After extraction the complex is converted to theAlCl form by addition of HCl. The complex and aromatics are separated bycrystallization, while the complex is in the AICL- form.

Referring now to FIG. 2, numeral 100 designates an extraction towerprovided with a temperature adjusting means 101 by way of which thetemperature in the extraction tower 100 is adjusted. A suitabletemperature is maintained in extraction tower 100 for extraction of thefeed stream which is introduced by line 102 from a source not shown,while the preferred solvent [ArH- ][AlCl is introduced by line 103, andflows countercurrently to the feed stream introduced by line 102. Theextraction tower 100 besides being equipped with temperature adjustingmeans is equipped with liquid liquid-contacting means such as bellcaptrays and the like.

In the extraction tower under suitable conditions there is formed aparaffinic phase which is removed by line 104 and is routed thereby intoa separator 105 where it is contacted with water introduced by line 106to wash the paraffin free of any aluminum chloride contained in anysolvent which may be removed by line 104. The water containing thealuminum chloride discharges by line 107, while the paraffins arerecovered by line 108.

The extract phase or solution is withdrawn by line 109 and dischargedthereby into an Oslo crystallizer 110 which is cooled by a pump-aroundsystem indicated by the numeral 111 and comprised of line 112 containinga pump 113, line 114 containing a heat exchanger 115, and line 116. Line116 contains a valve 117 and connects with line 118 which in turn formspart of pump-around system 111. The material in line 116 may bedischarged by line 118 by opening valve 119 therein.

In the bottom of the Oslo crystallizer 110 there exists a phase ofliquid aromatics and solids which are discharged by line 120 into acentrifuge 121 whereby a filtrate is removed by line 118 controlled byvalve 122 and solids by line 123' which are discharged thereby into amelt drum 124 provided with a heating jacket 125 equipped with lines 126and 127 for circulating heating fluid therethrough to melt the solidphase which comprises the complex [ArI-I][AlCl,] which is removed byline 128 as a liquid and which discharges into line 129 and recycled tothe extraction tower 100 by line 103. Line 129 is provided with a valve130 for discharge of the liquid complex if desired and valve 131 forintroducing make-up complex as may be required.

The recycle stream in the Oslo crystallizer 110 may have a branch line132 provided with a valve 133 for discharge of the product by way ofline 134 controlled by valve 135. In this case the product withdrawnthrough valve 135 is treated with water in a vessel similar to vessel 27in FIG. 1 and the water and product withdrawn as described therein. Line134 may connect by line 136 containing a valve 137 to extraction tower100 for supplying reflux thereto.

It will be seen from the foregoing brief description that a rich extractsolution is charged to an Oslo crystallizer system. A recycle stream ofhydrocarbon is cooled to provide refrigeration. In this system a mostinteresting phase transformation occurs on crystallization. The solventis removed by crystallization rather than is the solute. Hence, as aportion of the complex crystallizes out the remaining solution issupersaturated with respect to the desired product labeled BTX andtherefore a proportionate amount of liquid hydrocarbon phase appears.This results in the presence of one solid and two liquid phases. Thesupernatant liquid may be drawn off from the crystallizer essentiallyfree of complex by line 112 containing valve 140. The slurry of solidcomplex and liquid discharges to a centrifuge with the filtrate beingrecycled as described, while the solids are melted and returned to theextraction system.

Two stage crystallization may be used and the separated hydrocarbon fromthe first stage may have a higher concentration of nonaromatics than thetotal extract and, hence, this constitutes a reflux stream. The secondstage hydrocarbon constitutes the BTX product and is purer than thetotal extract.

It will be clear from the description taken with the drawing (FIGS. 1and 2 and particularly FIG. 2) that two types of extraction solvent maybe used. The mol ratios of aromatic to HCl to AlCl are 1:122 and 1:1:1for the two solvents. The former may be referred to as a dimer solvent[ArH] [Al Cl,] and the latter may be referred to as a monomer solvent[ArH][AlCl The present invention allows the obtaining of new, useful andunobvious results and therefore is a step forward in the art.

It will be seen from the brief description taken with the drawing that anew and unobvious process for separating paraffinic hydrocarbons hasbeen devised. The invention is unobvious since heretofore it was notknown that such could be done.

The nature and objects of the present invention having been completelydescribed and illustrated and the best mode contemplated set forth, whatI wish to claim as new and useful and secure by letters Patent is:

l. A process for separating aromatic hydrocarbons from aparaffin-aromatic hydrocarbon mixture which comprises:

contacting said mixture at a temperature wherein a .liquid paraffinichydrocarbon phase and a liquid aromatic hydrocarbon phase is formed witha solvent characterized by the formula:

said solvent consisting of a solution of a different aromatichydrocarbon (Ar) dissolved in the same different aromatic hydrocarbon inits protonated form with aluminum chloride and present in about equalmolar amounts, said aromatic hydrocarbon (Ar) being at least as basic asany of the aromatic hydrocarbons to be separated from saidparaffin-aromatic hydrocarbon mixture:

separating said paraffinic hydrocarbon phase from said aromatichydrocarbon phase; adding HCl to said aromatic hydrocarbon phase at atemperature wherein said HCl and solvent reacts in accordance with thefollowing equation;

Ar [ArH] [Al Cl,] HCl 2[ArH][AlCl ]said [ArH][AlCl being a solid at saidtemperature; and

separating said aromatic hydrocarbons from said solid [ArH][AlCl 2. Aprocess in accordance with claim 1 in which the mixtures are admixed ata temperature from about 0 to about 80 C.

3. A process in accordance with claim 1 in which Ar is mesitylene and inwhich the paraffin-aromatic hydrocarbon mixture comprises benzene,toluene, xylenes, and paraffins and naphthenes of similar boiling range.

4. A process in accordance with claim 1 in which the HCl is added at atemperature within the range of 80 C. to about 20 C.

5. A process in accordance with claim 1 in which separated aromatichydrocarbons are treated with water. 6. A process in accordance withclaim 1 which HCl is separated from the solid to form Ar [Arl-l] [Al,Cl-

which is recycled to be used as said solvent.

7. A process in accordance with claim 6 in which the HCl is separated byheating and pressure reduction.

8. A process in accordance with claim 6 in which the HCl is separated bypressure reduction.

9. A process in accordance with claim 7 in which the solid is heated toa temperature from about -80 C to about 80 C and the pressure is reducedfrom about at least one atmosphere to about 0.1 atmosphere.

10. A process for separating aromatic hydrocarbons from aparaffin-aromatic hydrocarbon mixture which comprises:

contacting said mixture at a-temperature wherein a liquid paraffinichydrocarbon phase and a liquid aromatic hydrocarbon phase is formed witha liquid solvent characterized by the formula:

said solvent consisting of a different aromatic hydrocarbon in itsprotonated form with aluminum chloride and present in about equal molaramounts, said aromatic hydrocarbon (Ar) being at least as basic as anyof the aromatic hydrocarbons to beseparated from said mixture;

separating said paraffinic hydrocarbon phase from said aromatichydrocarbon phase containing said solvent; chilling said aromatichydrocarbon phase containing said solvent to a temperature sufi'icientto form a solid solvent phase at said chilled temperature; andseparating said solid solvent phase from said aromatic hydrocarbonphase.

11. A process in accordance with claim 10 in which the solid solventphase is melted to obtain said solvent in its liquid form.

12. A process in accordance with claim 10 in which the differentaromatic hydrocarbon is selected from the group consisting ofmesitylene, isodurene, pentamethyl-benzene, and hexamethylbenzene.

13. A process in accordance with claim 11 in which the solvent isconverted to the form Ar+[ ArH][Al,Cl,] by removal of HCl therefrombefore it contacts said mixture.

'14. A process in accordance with claim 13 in which the aromatichydrocarbon phase is treated with HCl.

2. A process in accordance with claim 1 in which the mixtures areadmixed at a temperature from about 0* to about 80* C.
 3. A process inaccordance with claim 1 in which Ar is mesitylene and in which theparaffin-aromatic hydrocarbon mixture comprises benzene, toluene,xylenes, and paraffins and naphthenes of similar boiling range.
 4. Aprocess in accordance with claim 1 in which the HCl is added at atemperature within the range of -80* C. to about 20* C.
 5. A process inaccordance with claim 1 in which separated aromatic hydrocarbons aretreated with water.
 6. A process in accordance with claim 1 which HCl isseparated from the solid to form Ar + (ArH) (Al2Cl7) which is recycledto be used as said solvent.
 7. A process in accordance with claim 6 inwhich the HCl is separated by heating and pressure reduction.
 8. Aprocess in accordance with claim 6 in which the HCl is separated bypressure reduction.
 9. A process in accordance with claim 7 in which thesolid is heated to a temperature from about -80* C to about 80* C andthe pressure is reduced from about at least one atmosphere to about 0.1atmosphere.
 10. A process for separating aromatic hydrocarbons from aparaffin-aromatic hydrocarbon mixture which comprises: contacting saidmixture at a temperature wherein a liquid paraffinic hydrocarbon phaseand a liquid aromatic hydrocarbon phase is formed with a liquid solventcharacterized by the formula: (ArH) (AlCl4) said solvent consisting of adifferent aromatic hydrocarbon in its protonated form with aluminumchloride and present in about equal molar amounts, said aromatichydrocarbon (Ar) being at least as basic as any of the aromatichydrocarbons to be separated from said mixture; separating saidparaffinic hydrocarbon phase from said aromatic hydrocarbon phasecontaining said solvent; chilling said aromatic hydrocarbon phasecontaining said solvent to a temperature sufficient to form a solidsolvent phase at said chilled temperature; and separating said solidsolvent phase from said aromatic hydrocarbon phase.
 11. A process inaccordance with claim 10 in which the solid solvent phase is melted toobtain said solvent in its liquid form.
 12. A process in accordance withclaim 10 in which the different aromatic hydrocarbon is selected fromthe group consisting of mesitylene, isodurene, pentamethyl-benzene, andhexamethylbenzene.
 13. A process in accordance with claim 11 in whichthe solvent is converted to the form Ar+(ArH)(Al2Cl7) by removal of HCltherefrom before it contacts said mixture.
 14. A process in accordancewith claim 13 in which the aromatic hydrocarbon phase is treated withHCl.